The fuel system of every engine, of course, requires appropriate means to regulate the quantity of both air and fuel and to provide a properly mixed air/fuel mixture to the engine. Liquid fuel, having been drawn from a fuel tank by a fuel pump and delivered through various filters will ultimately arrive at a carburetor where the fuel is measured and mixed with air. At this point, the liquid fuel begins to vaporize. If the liquid fuel is not fully vaporized, it can form puddles along the intake manifold, will not appropriately burn, and the cylinders fartherest from the carburetor will receive too lean a mixture. One known technique to aid with this vaporization is to place the carburetor itself directly on top of the intake manifold with that portion of the intake manifold in turn being placed directly on top of the exhaust manifold so that rising heat from the exhaust manifold creates a "hot spot" in the intake manifold which helps vaporization occur. The more completely the fuel is vaporized in the air, the more even its distribution within the fuel mixture and to each of the cylinders.
It is also known that gasoline evaporates more rapidly in a partial vacuum than it does at atmospheric pressures, and the rate of evaporation depends, in part, upon the degree of vacuum in the intake manifold itself. As engine speeds increase, such as when the throttle is fully open, there may be so little vacuum that some of the fuel remains in liquid form and is either carried along in droplets by the in rushing air or will flow along the walls of the intake manifold.
Over the years, a number of concepts have been developed to assist the vaporization of the fuel and each of these various concepts has involved heating the area where vaporization is to occur in order to improve fuel vaporization. The source of heat for this purpose generally is developed from one of three sources, either through separate electric heaters, hot coolant or hot exhaust gases.
Two references that deal with the use of electric heating elements to help fuel vaporization include Jordan, U.S. Pat. No. 3,930,477 and Granger, U.S. Pat. No. 4,379,443. Jordan shows the use of a resistance heating element in combination with an injector nozzle. The heating element is the form of a cylindrical element positioned in the intake manifold adjacent an intake valve operative to emit an air/fuel mixture into a cylinder. With the heating element positioned between the fuel injector and that intake valve, fuel injected is immediately exposed to radiant heat from the electric element and is vaporized.
In Granger, a hollow housing is employed with the housing including an interior baffle plate. The housing includes openings in the upper and lower walls and the intermediate baffle plate can either include a plurality of openings across its surface or at least one marginal portion of that baffle is spaced from an opposing sidewall of the housing. The baffle is used to establish turbulence within the air/fuel mixture flowing through the heating element in order to promote a more complete vaporization of the fuel in the fuel and air mixture. Included as well within the housing, is an electrical heating coil with portions of the heating coil being in registry with openings on one side of the housing.
Vaporizing approaches using the hot coolant liquids are Hollabaugh, U.S. Pat. No. 3,150,652 and Wood, U.S. Pat. No. 4,029,065. Hollabaugh states that the coolant from his liquid cooled engine, which frequently exceeds 180.degree. F., is employed to heat a hollow chamber that surrounds passageways through which the air/fuel mixture will flow in order to thereby promote fuel vaporization. The structure in Hollabaugh includes a fairly thin chamber that is mounted between the carburetor and the intake manifold.
In Wood, the heating device is in the form of a mounting plate in which two through bores have been cut to axially align with the barrels of the carburetor, the device being inserted between the carburetor and the throttle body. The device includes a conduit structure which passes into the device, through each of the two through bores, out the opposite side. Within each of the bores, a series of fins extend transversely thereacross and in an axial direction with respect to the coolant conduit. The air/fuel mixture will pass over both the conduit and the fins and, accordingly, the heat exchanger effect will aid and enhance fuel vaporization.
With respect to the use of exhaust gases as a source of heat, the patents I am aware of are Shum, U.S. Pat. No. 1,269,753; Christian, U.S. Pat. No. 3,042,016; Finley et al, U.S. Pat. No. 4,167,165 and Varner et al, U.S. Pat. No. 4,167,166.
Shum relates to a fuel vaporizer comprised of a pipe extending through the sidewalls of the intake manifold with fins being provided along that pipe. The pipe is connected directly to the exhaust system, so that exhaust gases will flow through the pipe and heat the fins. Consequently, the air/fuel mixture passing through the intake manifold will likewise be heated by its direct passage over the pipe and fin structure.
In a somewhat similar manner, Finley et al relates to a direct heat exchange device that will also be placed in the air/fuel stream with the exhaust gas passing through heat exchange tubes, around which fins are formed, with the air/fuel mixture passing over those tubes and thus heated. The heat exchange tubes also extend perpendicularly to the flow direction of the air/fuel mixture.
Christian also discloses a block structure, insertable beneath the carburetor that is provided with two through bores. In a manner somewhat similar to Wood, a conduit extends through the sidewall of the insert device and passes through both of the through bores and then back out through the same side of the block where it entered. One end of the conduit is connected to the exhaust manifold so that products of combustion can be withdrawn therefrom. The other end terminates directly to the atmosphere or, as stated in the patent, "may deliver the exhaust gases to any other desired and suitable destination."
In Varner et al, the object is to insert hot air into the carburetor bore to help vaporize the air/fuel charge prior to its induction into the engine. The air is introduced at a very low flow rate and is comprised of highly heated auxiliary air. Delivery occurs through distributor pipes that produce a defused and uniform flow rate with respect to each of the carburetor barrels. This is accomplished by using perforated distributor tubes each mounted within a spacer block mounted below the carburetor, atop the intake manifold, with the tubes themselves located within a respective one of the Venturi openings.